A method for preparing quick-frozen, freeze-substituted cells for transmission electron microscopy and immunocytochemistry

A quick-freeze, freeze-substitution method is described which employs glutaraldehyde as well as osmium tetroxide (OsO4) in a 'double-fixation' protocol comparable to that used for conventional transmission electron microscopy. Cultured cells are quick-frozen in Freon 22 and freeze-substituted in an ethanolic solution of glutaraldehyde. Specimens destined for TEM are postfixed in OsO4 in acetone, embedded in Epon-Araldite, and sectioned. This method yielded ultrastructural preservation which was comparable to that obtained from methods employing OsO4 alone as a freeze-substitution fixative. However, if glutaraldehyde is used alone as a freeze-substitution fixative, specimens can be processed for immunocytochemistry without additional treatment with permeabilizing agents.